The present invention relates generally to refrigeration compressors and more specifically to such compressors incorporating shields for reducing the lubricating oil level in the area surrounding the rotating rotor during operation.
Typical refrigeration compressors incorporate a lubricant sump in the lower or bottom portion of the housing into which the drive shaft extends so as to pump lubricant therefrom to the various portions requiring lubrication. In addition, the lubricant also often acts to aid in removal of heat from the various components. In order to insure sufficient lubricating oil is contained within the sump to assure adequate lubrication and/or cooling of the moving parts while also minimizing the overall height of the housing, it is sometimes necessary that the oil level extend above the rotating lower end of the rotor. However, the higher viscosity of the oil as compared to refrigerant gas creates an increased drag on rotation of the rotor resulting in increased power consumption. This problem is further aggravated in scroll-type compressors which typically employ a counterweight secured to the lower end of the rotor.
U.S. Pat. No. 4,895,496 discloses a cup-shaped shield member which projects above the oil level in the sump and is positioned in surrounding relationship to the lower end of the rotor via a close fit with the drive shaft whereby the oil level in the area within the shield is reduced by the initial rotation of the rotor upon startup and return oil flow into this area is greatly restricted. Thus, the oil induced drag on the rotor and resulting increased power consumption of the motor is greatly reduced. In one embodiment, a rotation inhibiting projection is provided on the shield while in another embodiment the shield is allowed to rotate with the drive shaft although the speed of rotation thereof will be substantially less than that of the drive shaft due to the drag exerted thereon by the lubricant. In both embodiments, however, the power consumption of the motor is greatly reduced thus resulting in significant improvement in the operating efficiency of the compressor.
While the above described shield does reduce motor power consumption by substantially eliminating the viscous drag of the oil on the rotor, it also reduces the amount of oil being circulated across the lower end turns of the stator. In some applications, it may be desirable to achieve the advantages of this higher operating efficiency while also maintaining a substantial flow of oil across the stator end turns for cooling of same.
The present invention provides an improved shield which is carried by the drive shaft and allowed to freely rotate therewith. This improved shield incorporates a generally flat circular disk or flange positioned in close proximity to the lower end of the rotor which serves to restrict return flow of oil to the area of the rotating rotor and/or counterweight but still enables some circulation thereof which thereby increases the circulation of oil across the adjacent stator end turns. In operation, it has been found that this improved shield has resulted in improved cooling of the stator end turns without any substantial effect on the overall operating efficiency of the compressor.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.